This invention relates to an apparatus and method for suppressing knocking in an internal combustion engine such as an automotive engine.
In an internal combustion engine, if the ignition timing is too far advanced, abnormal vibrations referred to as knocking may occur. Since knocking can damage the cylinders of an engine, many engines are equipped with a knock suppressing apparatus that senses the occurrence of knocking and then controls an engine operating parameter (such as the ignition timing) so as to suppress the knocking.
A typical knock suppressing apparatus is equipped with a knock sensor that is mounted on an engine. The knock sensor detects vibrations of the engine, including vibrations due to knocking, and generates a corresponding output signal. The output signal is amplified and processed to produce a vibration level signal indicative of the magnitude of the engine vibrations during prescribed periods of time when knocking is most likely to occur. The vibration level signal is compared with a threshold signal that is chosen so as to be higher than the background noise level of the vibration signal. When the vibration level signal exceeds the threshold signal, the knock suppressing apparatus determines that knocking is taking place and retards the ignition timing until knocking no longer occurs.
The vibration level signal and the threshold signal generally increase in magnitude as the engine rotational speed increases. Therefore, if the engine rotational speed varies over a wide range, the dynamic ranges of the vibration level signal and the threshold signal become very large, and the large dynamic ranges of these signals make it difficult to accurately detect knocking over the entire operating range of the engine.